Field of the Invention
This invention relates generally to vacuum heat treating furnaces and in particular to a heating element arrangement for a vacuum heat treating furnace.
Description of the Related Art
Prior to the present invention, a center heating element arrangement was used in a vacuum aluminum brazing furnace manufactured by Ipsen Inc., the assignee of the present application. A center heating element is a heating element bank that is positioned between two separate workloads inside a vacuum furnace. This arrangement allows for faster and more uniform heating of such loads because when the load is split into two sections, the center heating element radiates heat toward the inside-facing surfaces of the workloads while the peripheral heating elements radiate heat toward the outside-facing surfaces of the workloads. This has only been accomplished in the past by providing the center element bank with its own dedicated power terminals, variable reactance transformer power supply, and a thermocouple for effecting temperature control.
The known center heating element arrangement leaves something to be desired with respect to design and operational flexibility. The requirement for a separate power supply complicates the power supply requirements for the vacuum furnace and results in a more costly design. That design also requires more penetrations in the furnace wall. Also, the fixed-in-place nature of the known arrangement prevents the vacuum furnace from being used for larger-size workloads.
In view of the foregoing, it would be desirable to have a vacuum heat treating furnace that avoids the undesirable aspects of the known arrangement for a center heating element, while still providing the benefits of a center heating element. Moreover, it would also be desirable to have a vacuum heat treating furnace having a center heating element that does not have its own connections outside the vacuum furnace, no separate power transformer, and no separate control thermocouple. It is further desirable to provide a vacuum heat treating furnace having a center heating element that is readily removable so that work loads of different sizes can be heat treated in the furnace.